Interstitial cystitis (IC) is a common entity with significant quality of life effects. However, the exact prevalence and incidence of IC is unclear a prior attempts to address this used solely administrative claims data or referral patterns from tertiary care referral centers. In order to define the national prevalence and incidence of IC, we propose a study using nation-wide data pulled from the Veterans Affairs (VA) Medical Centers, the largest integrated health system in the country. The goals of this study are to identify every IC patient within the VA system, to dive deep into the medical records of these patients to confirm the diagnosis of IC using a combination of automated data pulls plus hand-abstraction, to determine what other comorbid conditions co-exist with IC, and to assess treatment patterns and outcomes. By normalizing these data to US nation-wide numbers, we will be able to estimate the US nation-wide incidence and prevalence of IC. We will also prospective enroll a subset of these patients in a cohort study obtaining valuable quality of life data, patient-reporte outcomes, and urine samples. From this, we will be able to better assess the impact of IC on day-to-day life of the patients. Using the urine samples, we will explore whether biomarkers we have already identified to predict IC flare can be used to confirm the diagnosis of IC. Specific Aims are (Aim 1) Identify national-level prevalence and incidence of interstitial cystitis among a socio-economically and racially diverse population; (Aim 2) Prospectively determine the association between interstitial cystitis and health related quality of life and other comorbid conditions through validated questionnaires; and (Aim 3) Explore urine-based biomarkers to diagnose IC. If successful, our project has the possibility, for the first time, of clearly definin national-level prevalence and incidence of IC along with valuable information on treatment patterns and outcomes, impact of IC on quality of life and other co-morbid conditions, and even validate a biomarker for IC diagnosis. In summary, this study, by using an innovative approach to tap into nation-wide data, holds the potential to shed tremendous light on a disease of which to date we know very little.